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		<h1 id="0110-scale-button">0110: Scale Button</h1>

<p>Today we’re going to look at the <code class="language-plaintext highlighter-rouge">Scale</code> button. Note that this is different from a <code class="language-plaintext highlighter-rouge">ScaleButton</code> which we worked with in <a href="./0047-scalebutton-and-volumebutton.html">post #0047</a>. Also, we won’t be stopping with just a simple demo. Instead, we’ll be using it as a springboard into a practical example that grew out of a request by Jan Hönig over on the <em>DLang</em> forum. Jan asked for a demo wherein a slider controls the position of a ball on a <code class="language-plaintext highlighter-rouge">DrawingArea</code>. So today, we’ll start with this simple example of a plain-jane <code class="language-plaintext highlighter-rouge">Scale</code> button and in the next blog post, we’ll go for the full-on demo Jan asked for.</p>

<h2 id="the-scale-button">The Scale Button</h2>

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		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/011_misc/misc_01_scale.d" target="_blank">here</a>.
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<p>First things first. Since we haven’t yet talked about the <code class="language-plaintext highlighter-rouge">Scale</code> button, let’s start by taking a look at the bare-bones version…</p>

<h2 id="imports">Imports</h2>

<p>Right at the top, we have a couple of new import statements:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">import</span> <span class="n">gtk</span><span class="p">.</span><span class="n">Scale</span><span class="p">;</span>
<span class="k">import</span> <span class="n">gtk</span><span class="p">.</span><span class="n">Range</span><span class="p">;</span>
</code></pre></div></div>

<p>Yup, the <code class="language-plaintext highlighter-rouge">Scale</code> module is needed so we can work with the <code class="language-plaintext highlighter-rouge">Scale</code> button. As to the <code class="language-plaintext highlighter-rouge">Range</code>, we’ll talk about that when we get to the <code class="language-plaintext highlighter-rouge">MyScale</code> class.</p>

<p>For now, here’s the `AppBox’:</p>

<h2 id="the-appbox-stuff">The AppBox Stuff</h2>

<p>Here’s the entire class (it’s very brief, so why not?):</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">class</span> <span class="n">AppBox</span> <span class="p">:</span> <span class="n">Box</span>
<span class="p">{</span>
	<span class="n">MyScale</span> <span class="n">myScale</span><span class="p">;</span>
	<span class="kt">int</span> <span class="n">localPadding</span> <span class="p">=</span> <span class="mi">0</span><span class="p">,</span> <span class="n">globalPadding</span> <span class="p">=</span> <span class="mi">10</span><span class="p">;</span>
	<span class="kt">bool</span> <span class="n">expand</span> <span class="p">=</span> <span class="kc">false</span><span class="p">,</span> <span class="n">fill</span> <span class="p">=</span> <span class="kc">false</span><span class="p">;</span>
	
	<span class="k">this</span><span class="p">()</span>
	<span class="p">{</span>
		<span class="k">super</span><span class="p">(</span><span class="n">Orientation</span><span class="p">.</span><span class="n">VERTICAL</span><span class="p">,</span> <span class="n">globalPadding</span><span class="p">);</span>
		
		<span class="n">myScale</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyScale</span><span class="p">();</span>
		<span class="n">packStart</span><span class="p">(</span><span class="n">myScale</span><span class="p">,</span> <span class="n">expand</span><span class="p">,</span> <span class="n">fill</span><span class="p">,</span> <span class="n">localPadding</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// this()</span>

<span class="p">}</span> <span class="c1">// class AppBox</span>
</code></pre></div></div>

<p>All we’re doing here stuffing in an instance of a ‘MyScale’ class (derived from the <code class="language-plaintext highlighter-rouge">Scale</code>). That’s it.</p>

<p>So, let’s talk about that…</p>

<h2 id="the-myscale-class">The MyScale Class</h2>

<p>Here’s the class:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">class</span> <span class="n">MyScale</span> <span class="p">:</span> <span class="n">Scale</span>
<span class="p">{</span>
	<span class="kt">double</span> <span class="n">minimum</span> <span class="p">=</span> <span class="mi">0</span><span class="p">;</span>
	<span class="kt">double</span> <span class="n">maximum</span> <span class="p">=</span> <span class="mi">10</span><span class="p">;</span>
	<span class="kt">double</span> <span class="n">step</span> <span class="p">=</span> <span class="mi">1</span><span class="p">;</span>

	<span class="k">this</span><span class="p">()</span>
	<span class="p">{</span>
		<span class="k">super</span><span class="p">(</span><span class="n">Orientation</span><span class="p">.</span><span class="n">HORIZONTAL</span><span class="p">,</span> <span class="n">minimum</span><span class="p">,</span> <span class="n">maximum</span><span class="p">,</span> <span class="n">step</span><span class="p">);</span>
		<span class="n">addOnValueChanged</span><span class="p">(&amp;</span><span class="n">valueChanged</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// this()</span>
	
	
	<span class="kt">void</span> <span class="n">valueChanged</span><span class="p">(</span><span class="n">Range</span> <span class="n">range</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="n">getValue</span><span class="p">());</span>
		
	<span class="p">}</span> <span class="c1">// valueChanged()</span>

<span class="p">}</span> <span class="c1">// class MyScale</span>
</code></pre></div></div>

<p>Right up front in the class preamble, we set up the details. And those details are what define the <code class="language-plaintext highlighter-rouge">Range</code> I mentioned earlier:</p>

<ul>
  <li><code class="language-plaintext highlighter-rouge">minimum</code>,</li>
  <li><code class="language-plaintext highlighter-rouge">maximum</code>, and</li>
  <li><code class="language-plaintext highlighter-rouge">step</code>.</li>
</ul>

<p>The statement, <code class="language-plaintext highlighter-rouge">addOnValueChanged(&amp;valueChanged)</code> hooks up the <code class="language-plaintext highlighter-rouge">Scale</code> button to its callback function. If you look at the <code class="language-plaintext highlighter-rouge">valueChanged()</code> callback itself, you’ll see that the argument is a <code class="language-plaintext highlighter-rouge">Range</code>. So, let’s talk about that…</p>

<p>Firstly, the <code class="language-plaintext highlighter-rouge">Range</code> is internal, so don’t worry about figuring out how to access it. As the name implies, a <code class="language-plaintext highlighter-rouge">Range</code> is a series of numbers with a minimum and a maximum (we just saw those in the preamble). They can be 0 to 10, -52 to +76… whatever you want.</p>

<p>We saw similar things before in <a href="http://localhost:4000/posts/0047-scalebutton-and-volumebutton.html">the <code class="language-plaintext highlighter-rouge">ScaleButton</code> demo</a>, but as we’ve seen here, these two widgets are quite different. Don’t let the similarity in name throw you off.</p>

<h2 id="conclusion">Conclusion</h2>

<p>That’s all we have time for today, so join us next time when we put this <code class="language-plaintext highlighter-rouge">Scale</code> button to work in controlling the position of a simple graphic on a <code class="language-plaintext highlighter-rouge">DrawingArea</code>.</p>

<p>Until then.</p>

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